1. Field of the Invention
This invention relates to a pressure control valve unit for a hydraulic brake device for vehicles equipped with an antilock brake system (ABS) or a traction control system (TCS).
2. Description of the Related Art
A hydraulic brake device that can electronically control the brake pressure to prevent the wheels from locking during a sudden braking operation or a sudden acceleration is publicly known. It is known that the alternate opening and closing of the solenoid-type inlet and outlet valves in that type of device is accompanied by an abnormal noise, referred to as noise, vibration, and harshness (NVH), and vibration.
One proposed means to eliminate this NVH is to place a pressure-actuated switching valve on either the downstream or upstream side of the inlet valve in the main brake line. During an antilock or traction control operation, this switching valve would block the main brake line and switch the brake fluid to a constricted line. In this proposed means, however, when the valve mechanism of the switching valve blocks the main brake line and the valve is switched to the constricted channel, a gap is created between the valve plug and the valve seat comprising the valve mechanism, thus facilitating leakage of brake fluid. This leakage creates fluctuations in the constricted flow of brake fluid and pressure control becomes unreliable.